(178g) Structural and Dynamic Properties of Interfacial Water at the Silica Surface

The molecular structure of interfacial water at the silica solid surfaces was investigated by conducting equilibrium molecular dynamics simulations. Three crystallographically equivalent SiO2 substrates are considered. Different degrees of surface hydroxylation where employed to assess the effect of the surface chemistry on the structure of interfacial water. The degree of hydroxylation of the unsaturated oxygen atoms varied from 100, 50, and 0%, respectively. The SPC/E model was used to model water-water interactions. Density profiles, in-plane radial distribution functions, in-plane density distribution, hydrogen bond profiles, residence probability, reorientation correlation functions, and hydrogen bond lifetime were calculated to quantify the structural and dynamic behavior of water. Our results show that the surface hydroxylation affects the structure, orientation, hydrogen bond network, and dynamic behavior of interfacial water molecules. Data analysis suggests that the degree of hydroxylation controls the amount of water molecules in the first interfacial layer as well as the distance between the first adsorbed layer and the substrate. Well-organized and uniform structures of interfacial water appear on the homogeneously hydroxylated surface, while a heterogeneous interfacial structure, characterized by extensive water-water hydrogen bonds, forms on the partially hydroxylated surface. We demonstrate that both the local surface chemistry and water-water hydrogen bonds are the dominant factors that determine the structural properties of interfacial water. Atomic force microscopy experiments were also performed for the investigation of interfacial water on quartz. The data collected were analyzed with the Brownian force profile reconstruction technique.